Like a call made using a mobile telephone, with speech communication in a mobile communication system, currently, communication using a monaural scheme (monaural communication) is mainstream. However, hereafter, like a fourth generation mobile communication system, if the transmission rate becomes a still higher bit rate, it is possible to ensure a bandwidth for transmitting a plurality of channels, so that it is expected that communication (stereo communication) using a stereo scheme will be also spread in speech communication.
For example, when it is considered that the current situation where the number of users increases who enjoy stereo music by recording music in a mobile audio player provided with a HDD (hard disc) and attaching earphones or headphones for stereo to the player, in the future, it is expected that mobile telephones and music players will be linked together and a life style will be prevalent where speech communication is carried out using a stereo scheme utilizing equipment such as earphones and headphones for stereo. Further, in an environment such as video conference that has recently become widespread, in order to enable conversations having high-fidelity, it is expected that stereo communication is performed.
On the other hand, in a mobile communication system and wired communication system, in order to reduce load of the system, it is typical to achieve a low bit rate of transmission information by encoding speech signals to be transmitted in advance.
As a result, recently, a technique for coding stereo speech signals attracts attention. For example, there is a coding technique for increasing the coding efficiency for encoding predictive residual signals to which weight of CELP coding for stereo speech signals is assigned, using cross-channel prediction (refer to non-patent document 1).
Non-patent document 1: S. A. Ramprashad, “Stereophonic CELP coding using cross channel prediction,” In Proc. of the 2000 IEEE Workshop, pp. 136-138, 2000